This course material is about Gerris, a general-purpose fluid mechanics code developed by [[User:Popinet|St&eacute;phane Popinet]] at NIWA, Wellington, New Zealand. Gerris is a free, GPL-licensed, open source code available at [http://gfs.sf.net http://gfs.sf.net].

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The intended audience is typical first-year science or engineering graduate students with either very little experience of C or with some Fortran knowledge, but willing to work hard and learn. The student should know simple C data types, pointers and functions but not structures.

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This course is about Gerris, a general-purpose fluid mechanics code developped by Stephane Popinet at NIWA, Wellington, New Zealand .

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[[User:Zaleski|S. Zaleski]] has taught the course several times in Paris. In the actual course a lot of talking is done in addition to the material here. Each session is 30 minutes + 15 minutes of questions.

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The intended audience is typical first year graduate students with very little experience of C or some Fortran knowledge, but willing to work hard and learn.

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Gerris is a free, open source code available at [[http://gfs.sf.net]] .

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#[[Introduction to Gerris Programming]]

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#[[The Fully Threaded Tree]]

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== Course 1 ==

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#[[The Fluid Domain]]

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#[[Programming the Advection Scheme]]

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#[[The Gerris Object System]]

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=== Introduction ===

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#[[An Example of Use of the Gerris Object System]]

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#[[GfsView]]

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#[[Values, macros and structures in Gerris]]

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This course is about how Gerris ([[http://gfs.sf.net]] ) is programmed. It is intended to help in understanding the Gerris source code and learning how to modify it usefully.

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This course is not about the numerical methods in Gerris (however it would be good for students of this course to learn about them, for instance in the J. Comput. Phys. article) .

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Gerris is closely linked to Gts, the GNU triangulated surface library, also written by Stephane Popinet

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Gerris and Gts are programmed in a style analogous to that of Glib, Gnome and GTK . It is a style of C programming that offers several advantages:

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* Most aspects of Object-Oriented Programming (OOP) , such as the existence of classes with their own methods and inheritance.

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* The ability to interface to other programming languages. (As far as I know, this feature is not used in Gerris/Gts)

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To implement Object-Oriented Programming, Gerris/Gts uses its own “Object system”. This system is analogous to the Glib object system (Gobject), but not identical to it. Learning more about Gobject can be very useful.

There is no good order in which to read the code (I have not found it yet)

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==== Keep a C precedence and associativity table nearby ====

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A lot of macros and functions such g_assert come from the Glib.

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Keep a bookmark to the Glib documentation: [[http://library.gnome.org/devel/glib/unstable/index.html]]

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=== C basics ===

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==== Introduction to Structures ====

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<pre>

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struct Point {

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char name;

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double x, y;

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};

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</pre>

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An example of usage

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<pre>

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﻿main()

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{

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struct Point my_point; /* declaration */

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my_point.x = 0. ;

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my_point.y = 1.;

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my_point.name = ‘A’;

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}

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</pre>

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name, x and y are members of the structure of type “Point” called my_point. We also give it a name that can be exported (printed, passed to other functions) as a character. This example shows why it is useful to use structures to store several relevant informations or data together.

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==== An example: the structure GfsNorm in Gerris ====

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<pre>

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struct _GfsNorm {

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gdouble bias, first, second, infty, w;

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};

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typedef struct _GfsNorm GfsNorm

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</pre>

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From ''domain.h''.

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<pre>

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﻿GfsNorm gfs_domain_norm_residual (GfsDomain * domain,

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FttTraverseFlags flags,

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gint max_depth,

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gdouble dt,

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GfsVariable * res)

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{

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GfsNorm n;

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gpointer data[2];

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g_return_val_if_fail (domain != NULL, n);

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g_return_val_if_fail (res != NULL, n);

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gfs_norm_init (&n);

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data[0] = res;

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data[1] = &n;

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gfs_domain_cell_traverse (domain, FTT_PRE_ORDER, flags, max_depth,

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(FttCellTraverseFunc) add_norm_residual, data);

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#ifdef HAVE_MPI

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domain_norm_reduce (domain, &n);

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#endif /* HAVE_MPI */

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gfs_norm_update (&n);

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dt *= dt;

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n.bias *= dt;

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n.first *= dt;

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n.second *= dt;

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n.infty *= dt;

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return n;

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}

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</pre>

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From ''domain.c''

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Notice the use of

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* glib basic types ''gdouble, gpointer''

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* glib functions ''g_return_val_if_fail''

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==== Structures that are related to other structures ====

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Current revision

Preamble

This course material is about Gerris, a general-purpose fluid mechanics code developed by Stéphane Popinet at NIWA, Wellington, New Zealand. Gerris is a free, GPL-licensed, open source code available at http://gfs.sf.net.

The intended audience is typical first-year science or engineering graduate students with either very little experience of C or with some Fortran knowledge, but willing to work hard and learn. The student should know simple C data types, pointers and functions but not structures.

S. Zaleski has taught the course several times in Paris. In the actual course a lot of talking is done in addition to the material here. Each session is 30 minutes + 15 minutes of questions.